Integrated circuit with a sensor element for providing an encoded output signal

ABSTRACT

The invention relates to an integrated circuit with a single sensor element ( 1 ) for converting a physical variable into an electrical signal, comprising a comparator unit ( 4 ) by which means the electrical signal of the sensor element ( 1 ) can be compared with various different threshold values in order to produce different discreet circuit states and an output unit ( 5 ) for outputting an output signal representing the different discreet circuit states or the comparator unit ( 4 ). The threshold values of the comparators of the comparator unit ( 4 ) are stored in a storage unit of the integrated circuit in such a way that they can be regulated with a control device ( 3 ). The integrated circuit has a single output terminal ( 7   a ) on which the various circuit states of the electrical signal can be picked off in code.

BACKGROUND OF THE INVENTION

The invention relates to an integrated circuit arrangement with a sensorelement, and in particular to an integrated circuit sensor such as amagnetic field transducer that provides an encoded output signal on anintegrated circuit lead.

Integrated circuit arrangements with sensor elements (e.g. with magneticsensors) that detect mechanical switching states in a large number ofconsumer and automotive applications are known. They detect a mechanicalswitching state by a variable magnetic field, which represents thechanged position on the basis of a variable distance between themagnetic field sensor and a movable magnet. The physical variable ofmagnetic field strength is thus used as a measure for determining theswitching state. If the magnet approaches the transducer, which convertsthe magnetic field strength into an analog electrical signal, theswitching state “turned on” is represented at the output of the sensorcircuit when the distance becomes less than a certain distance A1. Ifthe distance becomes less than a further distance A2, the output signalrepresents “turned off”. This clearly shows that this sensor circuit canrepresent a switching state as either “turned on” or “turned off”. Ifmore switching states are required, it is necessary to use a cascade ofsuch sensor circuits. However, this results in a complex circuitstructure that is relatively bulky, expensive and unreliable.Furthermore, such total circuits have a high EMC risk, which is a greatdisadvantage in the automotive field.

Therefore, there is a need for an integrated circuit sensor thatreceives an input signal and compares the input signal against a numberof threshold values to determine the switching state efficiently withinthe integrated circuit.

SUMMARY OF THE INVENTION

Briefly, according to an aspect of the present invention, an integratedcircuit sensor comprises a comparator that receives an input signal, andcompares the input signal against a plurality of predetermined thresholdvalues and provides a plurality of comparator output signals eachindicative of whether or not the input signal exceeds an associated oneof the plurality of predetermined threshold values. An output stagereceives the plurality of comparator output signals and encodes stateinformation associated with the plurality of comparator output signalsto provide on a integrated circuit lead an encoded output signalindicative of the state information associated with the plurality ofcomparator signals.

According to another aspect of the invention, an integrated circuitsensor comprises a transducer element that provides a transducer outputsignal and a comparator that receives the transducer output signal. Thecomparator compares a signal indicative of the transducer output signalagainst a plurality of adjustable threshold values and provides aplurality of comparator output signals each indicative of one of anassociated plurality of switching states. An output stage receives theplurality of comparator output signals and encodes switching stateinformation associated with the plurality of comparator output signalsto provide on a bi-directional integrated circuit lead an encoded outputsignal indicative of the state information associated with the pluralityof comparator signals.

According to yet another aspect of the invention, an integrated circuitsensor comprises a transducer element that provides a transducer outputsignal. An amplifier receives the transducer output signal and providesan amplified transducer output signal. A comparator network receives theamplified transducer output signal, and compares a signal indicative ofthe amplified transducer output signal against a plurality of adjustablethreshold values to determine a state of the amplified transducer outputsignal, and provides a plurality of comparator output signals indicativeof the state of the amplified transducer output signal. An output stagereceives the plurality of comparator output signals and encodesswitching state information associated with the plurality of comparatoroutput signals to provide on a integrated circuit lead an encoded outputsignal indicative of the state.

The inventive circuit arrangement, which can represent more switchingstates than only “turned on” or “turned off”, comprises a control unitto control the sensor circuit, and an input to which an analogelectrical signal is conducted.

The analog electrical signal corresponds to an analog physical variable,such as pressure, force, acceleration, magnetic field strength,electromagnetic field strength, temperature, light intensity, or thelike. This electrical input signal is compared with several thresholdsin an analytical unit or a comparator unit. If the value of the signalfalls above or below these individual thresholds, an output signal isgenerated that represents a number of different switching states, whichextend beyond the single switching state of “turned on” or “turned off”.The output signal is conducted from the analytical unit or comparatorunit to the output stage and is made available to the environment of thesensor circuit for further use.

The invention thus succeeds in representing various differentiatedswitching positions using a single sensor circuit, which comprises asingle control unit, a single analytical unit, a single output stage,and a single input, and which is especially simple, compact, andreliable. For example, this can be used in connection with thecontact-free picking off of the many positions of the wiper lever in anautomobile by Hall sensors and an appropriate, series-connected,inventive sensor circuit. The various positions of the wiper lever, suchas, for example, “off”, “on slow”, “on fast”, “on very fast”, or “timedoperation”, are converted by the integrated circuit arrangement of thepresent invention into an electrical output signal, which can uniquelyand discretely represent these many switching states.

Advantageously, a cascade arrangement of several sensor circuits, as isthe case in the prior art, can be dispensed with. This is associatedwith a considerable reduction of costs, of the space needed for thecircuits, of the complexity of the circuit and wiring, with a markedreduction of trouble-proneness, as a result of the reduction in thenumber of components, and with an improvement as regards EMCsensitivity, due to the reduction of EMC-sensitive components andEMC-generating components. The inventive sensor arrangement is thus bestsuited for the automotive field, which precisely has specialrequirements for EMC compatibility and compact arrangements.

In addition, this sensor circuit proves to be a universal sensorcircuit, since it can interact with various transducers for convertinganalog physical variables into analog electrical signals. In this case,the analog electrical signal only needs to be amplified and thenconducted to the input and matched to the thresholds, as appropriate.

In a preferred embodiment, the transducer for converting the analogphysical variable into an analog electrical input signal is connected tothe single input, and thus is integrated into the sensor circuit. Thismakes it possible to adapt the transducer and sensor optimally to theremaining sensor circuit, and thus to create a closed and standardizedsensor circuit, which no longer requires any specific adjustment by theuser. This eliminates difficulties associated with such a standardizedcircuit with a transducer, especially if the user, when adapting theoutput signal of the transducer to the remaining circuit does notcorrectly take into account the relationships with the threshold values.This regularly results in considerable problems regarding theunambiguous nature of the output signal and thus the representation ofthe plurality of discrete circuit states. Furthermore, it is nowpossible to design the standardized sensor circuit with a transducerespecially optimized as regards space and EMC, since the interactions ofthe transducer with the remaining sensor circuit can already be takeninto account in the design.

The sensor circuit preferably has an output stage with a single output.At this output, the plurality of discrete circuit states is represented,for example, by the pulse/pause ratio of the output signal or by adigital signal, which is not necessarily binary coded, or by an analogsignal, which has a number of signal steps, corresponding to theplurality of switching states. For example, if five switching states areto be represented, the pulse/pause ratio can vary between 5/1, 4/2, 3/3,2/4, and 1/5. Besides these examples, one can also conceive of otherways of representing the plurality of switching states with a singleoutput. The design of the sensor circuit with a single outputconstitutes a sensor circuit which is especially cost-optimized, since aplurality of parallel outputs need no longer be made available.

In another embodiment, the output stage has the same number of outputsas the number of different discrete switching states that must berepresented. This increased number of outputs, which correlate with thevarious switching states, makes it possible to turn various devices onor off simultaneously and independently, corresponding to the pluralityof various switching states. In this case, each output has associatedwith it a corresponding device. A typical application of such a sensorcircuit is its use with a multi-function switch, which can turn variousdevices on or off individually or jointly, depending on the position ofthe switch lever. Another typical application of such a sensor circuitis in combination with a brightness sensor, which, with increasingdarkness, selectively turns on more and more light sources, so as alwaysto assure sufficient illumination in an interior room. The individuallight sources are activated selectively by their own circuit output.

Besides the two extremes of a single output and the same number ofoutputs as there are switching states, it is also possible for thenumber of outputs to lie between these extremes. This represents acompromise between the most economical sensor circuit with a singleoutput and the technically optimized sensor circuit with many outputs,each of which is always actuated selectively.

According to a preferred design, the thresholds may be adjustable. As aresult, the circuit can be adapted to the particular externalcircumstances for forming the output signal as a function of theelectrical input signal, without creating a new, corresponding sensorcircuit. It is thus possible to adapt the circuit arrangement topossible time changes, such as aging effects, especially in thetransducer associated with the circuit arrangement. Productiontolerances or changes due to various use conditions, for example due totemperature effects and the like, can thus be taken into account simplyand economically. This considerably expands the field of application ofthe sensor circuit, by further increasing its functionality, withoutrequiring complex or expensive external circuits to adapt the outputsignal or the input signal. This results in a simple and reliable sensorcircuit, which is especially characterized by an economical and flexibledesign.

An especially preferred design of the sensor circuit makes it possiblefor the user to set the thresholds himself. This can be done in aspecial learning mode of the sensor circuit, in which the desiredswitching ranges of the sensor circuit are approached, and theanalytical unit in collaboration with the control unit determines thenecessary parameters of the threshold values and stores them in anappropriate memory, which in particular is designed as a non-volatilememory. This results in an especially flexible and universallyapplicable sensor circuit, which allows the user a large and manifoldfield of application.

The thresholds preferably are combined into threshold pairs, whichspecify a range of values with which a certain discrete switching stateis associated. These threshold pairs preferably are closely spaced, sothat the range in between, which does not necessarily have a particularswitching state associated with it, is kept very narrow. In this way,the sensor circuit generates clear and defined switching states overnearly the entire measurement range of the analog physical variable. Thechoice of threshold pairs makes it possible, in a simple way, tocharacterize uniquely and very reliably circuit switching states, andthus to design a very reliable sensor circuit.

The sensor circuit with the threshold pairs preferably is designed sothat a hysteresis exists between the individual threshold pairs. Thisassures that a defined switching state exists in the preferably narrowrange between the individual threshold pairs. If there are frequentsmall fluctuations about a threshold, this assures that the sensorcircuit will not constantly switch back and forth between the individualswitching states, which would be undesirable. This assures that thesystem will assume certain switching states very reliably andpersistently.

The sensor circuit preferably is designed such that it ignores briefchanges of the input signal and does not consider these for changing theswitching signal. Such a design does not indeed prevent short-term noisesignals, which can occur again and again in an electronic circuit,whether due to electromagnetic radiation from the outside or due toswitching interferences, but it does prevent their negative effects.This can be achieved by integrating or averaging elements at the input.This makes the sensor circuit especially insensitive to noise.

The sensor circuit preferably is designed as an integrated circuit,which is especially advantageous as regards EMC compatibility and smallsize. In particular, a sensor circuit with an integrated transducer inthe form of an integrated circuit proves to be a complete sensorcircuit, which requires very few pins, and thus also is very economicaland not very trouble-prone. Furthermore, such a complete sensor circuitproves to be extremely small. Its predestined application thus is in theautomotive field, since tight spatial circumstances and specialrequirements for EMC compatibility prevail there.

These and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of preferred embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustration of an integrated circuit sensor;

FIG. 2 is a plot of voltage versus time to illustrate switching of thevarious thresholds associated with the integrated circuit sensor; and

FIG. 3 is a block diagram illustration of an alternative embodimentintegrated circuit sensor.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram illustration of an integrated circuit sensor10. The sensor 10 includes a transducer 1, which converts an analogphysical variable, for example a temperature or a magnetic fieldstrength or a pressure, into an electrical signal, and conducts thissignal to an amplifier 2. The amplifier 2 provides an amplifiedelectrical signal on a line 6 to an analytical unit 4. The analyticalunit 4 has a plurality of comparators, each of whose respectivecomparator thresholds can be adjusted by a control unit 3. Theparameters for the. thresholds of the comparators in the analytical unit4 are stored in a memory (not shown) in the control unit 3, and are usedto control the comparator thresholds.

Depending on the relationship of the amplified signal on the line 6 tothe respective comparator thresholds, the analytical unit 4 generates anappropriate output signal from each of the comparators, and thecomparator output signals are provided to an output stage 5. The outputstage transforms the signals from the analytical unit 4 into an outputsignal, which is distributed among the four outputs 7 a, 7 b, 7 c, and 7d. Because there are different outputs 7 a, 7 b, 7 c, 7 d from theoutput stage 5, it is possible to actuate directly four differentdevices or also groups of devices, connected to the outputs 7 a, 7 b, 7c, 7 d, selectively and independently of one another. Therefore,depending on the magnitude of an analog physical variable, severaldevices can be turned on or off by the sensor circuit 10, independentlyof one another and without complicated additional decoder circuits.

FIG. 2 shows a switching process by way of example. FIG. 2 shows thetime progress of an analog measurement variable, in an arbitrary unit,as a solid line. This analog measurement variable falls from the value 1to its lowest point just below 0.4, and then again rises to a value ofabout 1. Three pairs of thresholds are shown, namely A11, A21; A12, A22;A13 and A23, such that:A11<A21<A12<A22<A13<A23FIG. 2 shows the progress of the output signal, which is shown as adashed line. The output signal shows three different, discrete switchingstates, the switching state 1, 2, and 3. If the analog measurementvariable lies within the interval A11 to A21, the diagram shows theswitching state 1. If the analog measurement variable lies in thethreshold interval between A12 and A22, the output signal assumes theswitching state 2. If the analog measurement variable lies within thethreshold interval A13 to A23, it assumes the switching state 3.

Furthermore, the plot of FIG. 2 shows that a hysteresis exists betweenthe threshold intervals formed through the threshold pairs. This assuresthat, when the analog measurement variable falls from an analog valuewithin the interval A13 to A23 to below the limit A13, the measurementstate is retained, until the upper limit of the next threshold intervalA12, A22 is reached. Only when the analog measurement variable falls tothe threshold A22, does the signal change from the switching state 3 tothe switching state 2. The like applies to a further drop to thethreshold A21, where the signal then changes from switching state 2 toswitching state 1. The like also applies to a rise of the analogmeasurement variable, where the original switching state is retaineduntil the lower limit of the next threshold interval is reached. Forexample, when the analog measurement variable rises from a value 0.4,corresponding to the threshold A11, across the threshold A21 until itreaches the lower threshold A12, the switching state 1 is retained, eventhough the threshold interval A11 to A21, corresponding to the actualswitching state 1, has been left behind. Upon reaching the thresholdA12, the signal assumes the switching state 2, and this is retainedduring a further rise of the analog measurement variable, until thisreaches the threshold A13. Then there is a transition from the switchingstate 2 to the switching state 3.

This structure of the thresholds as three threshold pairs, which arerespectively connected to one another through a hysteresis region, makesit possible to reliably represent three discrete switching states as afunction of a varying analog measurement variable. The presence ofhysteresis regions in particular assures a definite switch between theindividual switching states and prevents undesirable frequent switchingwhen there are fluctuations about a threshold. This makes the sensorcircuit into an especially reliable and readily handled circuitarrangement, which can uniquely represent a plurality of discreteswitching states.

FIG. 3 is a block diagram illustration of an alternative embodimentintegrated circuit sensor 50. However, the circuit 50 now has a singleoutput terminal 7 a, from which the various switching states of theelectrical signal can be picked off in coded form. This single outputterminal 7 a can also be used as the input terminal for adjusting thethresholds.

Although the present invention has been shown and described with respectto several preferred embodiments thereof, various changes, omissions andadditions to the form and detail thereof, may be made therein, withoutdeparting from the spirit and scope of the invention.

1. An integrated circuit sensor, comprising: a comparator that receivesan input signal, and compares said input signal against a plurality ofpredetermined threshold values and provides a plurality of comparatoroutput signals each indicative of whether or not said input signalexceeds an associated one of said plurality of predetermined thresholdvalues; and an output stage that receives said plurality of comparatoroutput signals and encodes state information associated with saidplurality of comparator output signals to provide on a integratedcircuit lead an encoded output signal indicative of said stateinformation associated with said plurality of comparator signals,wherein said output stage comprises means for generating said encodedoutput signal using pulse width modulation, wherein said stateinformation is encoded within said encoded output signal based upon thepulse/pause ratio of said encoded output signal.
 2. The integratedcircuit sensor of claim 1, comprising a control unit that includes amemory device that stores and provides said plurality of predeterminedthreshold values.
 3. The integrated circuit sensor of claim 2, whereinsaid memory device comprises a read/write memory device that allows saidplurality of predetermined threshold values to be changed and stored insaid read/write memory device.
 4. The integrated circuit sensor of claim2, comprising means for reading updated predetermined threshold valuesthat are input to said integrated circuit sensor through said integratedcircuit lead that also receives said encoded output signal, and forstoring said updated predetermined threshold values in said memorydevice, which provides said updated predetermined threshold values tosaid comparator for comparison against said input signal.
 5. Anintegrated circuit sensor, comprising: a magnetic field transducercomprising a Hall effect transducer that generates and provides an inputsignal; a comparator that receives said input signal, and compares saidinput signal against a plurality of predetermined threshold values andprovides a plurality of comparator output signals each indicative ofwhether or not said input signal exceeds an associated one of saidplurality of predetermined threshold values; an output stage thatreceives said plurality of comparator output signals and encodes stateinformation associated with said plurality of comparator output signalsto provide on a integrated circuit lead an encoded output signalindicative of said state information associated with said plurality ofcomparator signals; and a control unit that includes a memory devicethat stores and provides said plurality of predetermined thresholdvalues.
 6. The integrated circuit sensor of claim 5, wherein said memorydevice comprises a read/write memory device that allows said pluralityof predetermined threshold values to be changed and stored in saidread/write memory device.
 7. The integrated circuit sensor of claim 5,comprising means for reading updated predetermined threshold values thatare input to said integrated circuit sensor through said integratedcircuit lead that also receives said encoded output signal, and forstoring said updated predetermined threshold values in said memorydevice, which provides said updated predetermined threshold values tosaid comparator for comparison against said input signal.
 8. Anintegrated circuit sensor, comprising: a transducer element thatprovides a transducer output signal; a comparator that receives saidtransducer output signal, and compares a signal indicative of saidtransducer output signal against a plurality of adjustable thresholdvalues and provides a plurality of comparator output signals eachindicative of one of an associated plurality of switching states; and anoutput stage that receives said plurality of comparator output signalsand encodes switching state information associated with said pluralityof comparator output signals to provide on a bi-directional integratedcircuit lead an encoded output signal indicative of said stateinformation associated with said plurality of comparator signals;wherein said output stage comprises means for generating said encodedoutput signal using pulse width modulation, wherein said stateinformation is encoded within said encoded output signal based upon thepulse/pause ratio of said encoded output signal.
 9. The integratedcircuit sensor of claim 8, wherein said comparator comprises hystersison each of said predetermined threshold values.
 10. An integratedcircuit sensor, comprising: a transducer element that provides atransducer output signal; an amplifier that receives said transduceroutput signal and provides an amplified transducer output signal; acomparator network that receives said amplified transducer outputsignal, and compares a signal indicative of said amplified transduceroutput signal against a plurality of adjustable threshold values todetermine a state of said amplified transducer output signal, andprovides a plurality of comparator output signals indicative of saidstate of said amplified transducer output signal; an output stage thatreceives said plurality of comparator output signals and encodesswitching state information associated with said plurality of comparatoroutput signals to provide on a integrated circuit lead an encoded outputsignal indicative of said state; and a control unit that includes amemory device that stores and provides said plurality of adjustablethreshold values.
 11. An integrated circuit sensor, comprising: atransducer element that comprises a magnetic field transducer andprovides a transducer output signal; an amplifier that receives saidtransducer output signal and provides an amplified transducer outputsignal; a comparator network that receives said amplified transduceroutput signal, and compares a signal indicative of said amplifiedtransducer output signal against a plurality of adjustable thresholdvalues to determine a state of said amplified transducer output signal,and provides a plurality of comparator output signals indicative of saidstate of said amplified transducer output signal; an output stage thatreceives said plurality of comparator output signals and encodesswitching state information associated with said plurality of comparatoroutput signals to provide on a integrated circuit lead an encoded outputsignal indicative of said state; and a control unit that includes amemory device that stores and provides said plurality of adjustablethreshold values.
 12. An integrated circuit sensor, comprising: amagnetic field transducer that generates and provides an input signal; acomparator that receives said input signal, and compares said inputsignal against a plurality of predetermined threshold values andprovides a plurality of comparator output signals each indicative ofwhether or not said input signal exceeds an associated one of saidplurality of predetermined threshold values; an output stage thatreceives said plurality of comparator output signals and encodes stateinformation associated with said plurality of comparator output signalsto provide on a integrated circuit lead an encoded output signalindicative of said state information associated with said plurality ofcomparator signals; and a control unit that includes a memory devicethat stores and provides said plurality of predetermined thresholdvalues.
 13. An integrated circuit sensor, comprising: a transducerelement comprising a magnetic field transducer that provides atransducer output signal; a comparator that receives said transduceroutput signal, and compares a signal indicative of said transduceroutput signal against a plurality of adjustable threshold values andprovides a plurality of comparator output signals each indicative of oneof an associated plurality of switching states; an output stage thatreceives said plurality of comparator output signals and encodesswitching state information associated with said plurality of comparatoroutput signals to provide on a bi-directional integrated circuit lead anencoded output signal indicative of said state information associatedwith said plurality of comparator signals; and a control unit thatincludes a memory device that stores and provides said plurality ofpredetermined threshold values.
 14. The integrated circuit sensor ofclaim 13, wherein said memory device comprises a read/write memorydevice that allows said plurality of predetermined threshold values tobe changed and stored in said read/write memory device.
 15. Theintegrated circuit sensor of claim 13, comprising means for readingupdated predetermined threshold values that are input to said integratedcircuit sensor through said integrated circuit lead that also receivessaid encoded output signal, and for storing said updated predeterminedthreshold values in said memory device, which provides said updatedpredetermined threshold values to said comparator for comparison againstsaid signal indicative of said transducer output signal.
 16. Anintegrated circuit sensor, comprising: a transducer element thatcomprises a magnetic field transducer and provides a transducer outputsignal; an amplifier that receives said transducer output signal andprovides an amplified transducer output signal; a comparator networkthat receives said amplified transducer output signal, and compares asignal indicative of said amplified transducer output signal against aplurality of adjustable threshold values to determine a state of saidamplified transducer output signal, and provides a plurality ofcomparator output signals indicative of said state of said amplifiedtransducer output signal; an output stage that receives said pluralityof comparator output signals and encodes switching state informationassociated with said plurality of comparator output signals to provideon a integrated circuit lead an encoded output signal indicative of saidstate; and a control unit that includes a memory device that stores andprovides said plurality of predetermined threshold values.
 17. Theintegrated circuit sensor of claim 16, wherein said memory devicecomprises a read/write memory device that allows said plurality ofpredetermined threshold values to be changed and stored in saidread/write memory device.
 18. The integrated circuit sensor of claim 16,comprising means for reading updated predetermined threshold values thatare input to said integrated circuit sensor through said integratedcircuit lead that also receives said encoded output signal, and forstoring said updated predetermined threshold values in said memorydevice, which provides said updated predetermined threshold values tosaid comparator for comparison against said signal indicative of saidamplified transducer output signal.